A number of different processes and systems are available for grinding or pulverizing solid materials such as coal, minerals and the like. One system of particular interest here is that disclosed in U.S. Pat. No. 4,579,288 (McDermid et al), the subject matter of which is hereby incorporated by reference. The McDermid et al patent discloses a pulverizer for pulverizing solid materials such as coal including a plurality of jet nozzles which direct high speed jets of air into a chamber so as to cause particles contained within the chamber to impact against each other to provide pulverization. A central "sleeve" mounted in the chamber divides the chamber into an inner central cylindrical chamber and an outer annular chamber, and with this arrangment, some of the heavier particles which rise upwardly within the inner chamber with the air currents created by the jets of air fall downwardly into the outer chamber to be re-entrained by the jet nozzles and recirculated for further pulverization. A further, similar pulverizer apparatus of interest is that disclosed in U.S. Pat. No. 4,553,704 (Wilson et al) while South African Patent No. 84/1061 also discloses similar subject matter. In addition, U.S. Pat. No. 4,219,164 discloses an earlier apparatus of this type. Other patents of more general interest include: South African Pat. No. 85/3488, relating to method and apparatus for operating a metallurgical furnace using pulverized fuel; South African Pat. No. 85/1838 relating to a method of operating a coal burner using pulverized coal; and South African Pat. No. 85/1839 relating to a coal burner assembly for burning ultrafine pulverized coal.
As discussed below, an important application of the pulverizer of the invention concerns production of ultrafine coal particles for use as an alternate fuel in oil or gas-fired boilers, and the literature in this field includes Progress Report on Dry Micronized Coal Application in a Gas-Fired Boiler, Koeroghlian; Industrial Power Conference; Chicago Ill., 1985.